Do you think is the right time to sell old GPU like RX470, RX480, GTX1070 ?
If you're currently mining and selling right away, then yes, it's the time for you to sell them. However, if you're having a macro-strategy, and you're not selling the coin right after mining it, then you should continue mining (of course, only if it's profitable and gives you in return your electric cost + some profit) and just forget about selling it.
most gamers don't want them if they were used for mining.
So true. In almost all of the GPU-buying related ads, gamers clearly mention that, "don't dare to contact me if you've used the card for mining!"
I've had this issue in the past when I actually was buying GPUs for mining, I didn't want any that was used in mining either.
The reason why is because the older GPUs like the 280X, they used massive power like 300 Watts per GPU. And most people who mined with those GPUs probably didn't have adequate cooling and the fans always ran at 90% and were near dead.
I noticed that most of the ones on the market however were mined with because the seller had no idea what the current gaming titles were or anything about high spec PC components like which i5 or i7 CPU to get, RAM speeds, etc.
However in the end its impossible to prove if it ever was mined with or not. Some non-mining GPUs can also have dead fans.
IMO, if the GPU passes the stress test, it proves that the GPU is still in a very good condition and can still live long enough; rest depends upon your luck.
Yes except most people won't let you test out the GPU prior to purchase unless you are buying on eBay.
Most private sales happen in public areas for security and nobody will bring their entire desktop computer with monitor and mouse.
90-95% of the time the Craiglist sales are honest however and they usually sell working GPUs, its the other 5% you need to worry about.
I bought and sold tons of equipment on Craiglist, if there is something wrong with a part like a dead fan, I usually document it.